Sugar transport and metabolism by Streptococcus mutans is directly related to the onset and development of the biofilm commonly called plaque, leading to the formation of human dental caries (tooth decay). In S. mutans, sugar substrates are taken up by ABC transporters and, more commonly, by phosphoenolpyruvate (PEP)-sugar phosphotransferase systems (PTSs). To better understand sugar transport and metabolism of this important dental pathogen, we have performed global transcriptional analyses of S. mutans UA159 using expression microarrays. Detailed transcriptional analyses of S. mutans showed the presence of five constitutively transcribed and eleven inducible sugar transporters. We have also defined the sugar-specificity for most of these transporters. This application proposes to obtain knowledge regarding the regulation of carbohydrate transport in S. mutans by focusing on PTS sugar transporters. We hypothesize that there is a regulation hierarchy among PTS sugar transporters; specifically that several PTSs are involved in the regulation of the other PTSs and that this regulation is carbohydrate-specific. Accordingly, we propose to: (Aim 1) Identify PTSs of S. mutans UA159 that control regulation of inducible PTSs, in planktonic cultures and in biofilms; and (Aim 2 and 3) Characterize the molecular mechanisms of PTS regulation in planktonic cultures and in biofilms. Since the uptake and metabolism of carbohydrates are the key steps in the formation and release of cariogenic acid, the completion of the proposed experiments will provide highly relevant information for understanding, and perhaps interfering with, the cariogenicity of S. mutans.